At an excavation site, a mine or the like for open-pit mining, work is generally performed including excavating a large amount of minerals and earth or sand by hydraulic excavators and loading a large amount of excavated minerals (crushed stones) and the like on large-sized haulage vehicles called “dump trucks” to haul them to an unloading site such as a port.
A large-sized dump truck that adopts an AC drive traction system drives a generator by an engine, and subsequent to control of the resulting electricity by an inverter, drives AC motors to perform traveling. As the generator produces heat as an energy loss due to the electric resistances of its parts and coils, there is a need to forcedly supply cooling air into the generator to perform cooling of the generator.
At a mine where large-sized dump trucks are in operation, impurities (hereinafter called “dust”) such as sand are contained abundantly in the atmosphere because of dust arisen by loaders and forerunning dump trucks. If dust-containing air is directly taken into a generator, a potential problem may therefore arise in that insulating coatings in the generator may be worn out by dust and the insulation resistance may be lowered. If the use of the generator is continued with its insulating coatings having been worn out, a potential problem may arise in that the wearing may proceed to complete loss of the insulating coatings, coils may eventually undergo dielectric breakdown, and a rotor may become no longer usable.
For the prolongation of the service life of such a generator, the removal of dust from cooling air is considered to be the most effective measure. However, a dust collector equipped with a filter requires scheduled maintenance, and moreover is accompanied by a concern about a possible reduction in cooling performance through the clogging of the filter.
As a technology that can remove dust from air without using any filter, Patent Document 1 is publicly known, for example. Patent Document 1 discloses a configuration that in a cooling unit for a drive system of a large-sized dump truck, strata tubes are parallelly arranged in an air cleaner that is disposed in an inlet part of the cooling unit. According to Patent Document 1, dust can be removed from cooling air by introducing the cooling air into the strata tubes and producing swirling flows in the strata tubes.